In humans, increases in rheumatoid factor (RF) production are associated with rheumatoid arthritis (RA) and other autoimmune phenomena, chronic viral and bacterial infections, and secondary antigen challenge. It is hypothesized that RF contribute to the lymphocyte hyperactivity and inflammation characteristic of RA and the regulation of ongoing antibody responses in normal subjects. This hypothesis is founded on the ability of RF to recognize autologous IgG; thus RF could contribute to the formation of biologically-active immune complexes (IC) or bind to surface immunoglobulin on B cells with regulatory consequences. The goals of this proposal are to investigate the mechanisms by which: i) RF-associated IC (RF-IC) polyclonally activate human B cells in vitro; ii) RF-IC induce cultured human mononuclear cells to produce arachidonic acid (AA) metabolites, some of which may function as inflammatory mediators and/or immunoregulatory molecules; and iii) monoclonal RF, free of IC, regulate mitogen- and antigen-induced human in vitro antibody responses. Experiments will be performed on cultured human peripheral blood mononuclear cells from both autoimmune patients and normal subjects in order to identify disease-specific patterns of reactivity to RF-IC and RF. Preliminary data suggest that RF-IC, isolated from the plasma of RA patients, are able to polyclonally activate normal human B cells and induce the release of AA metabolites from normal mononuclear cells in vitro. Therefore, studies will be carried out to physically characterize RF-IC from various sources (plasma, synovial fluid) and determine the cellular and subcellular parameters of B cell activation and AA metabolite release in the presence of these preparations. Other preliminary data indicate that a monoclonal human IgM RF is able to inhibit antigen- and mitogen-induced antibody responses in normal human lymphocyte cultures. Therefore, a panel of monoclonal IgM RF will be produced, characterized, and assessed for stimulatory and inhibitory effects on in vitro antibody responses. Studies will be initiated to address the mechanism by which these preparations regulate B cell function.